This invention relates to a steady rest for supporting a rotatable cylindrical workpiece undergoing a precision machining or grinding operation. More particularly this invention relates to a steady rest in which a pair of clamping members are moved toward a workpiece by camming a pair of parallel, slidably mounted plates (bars) in opposite directions along a linear path of motion. One plate supports one clamping member; the other plate supports the other clamping member.
Steady rests are commonly used in manufacturing for supporting a rotating cylindrical workpiece during a machining or grinding operation. Examples of steady rests may be found in U.S. Pat. Nos. 4,399,639; 4,647,097; 4,647,100; 4,650,237; 5,058,468; 5,237,780; and 5,285,599 all which name Richard J. Lessway as the inventor and which have been assigned to AROBOTECH Systems, Inc. of Madison Heights, Mich.
An example in which steady rests are employed is to support a large or heavy duty crankshaft that may be 3 to 12 feet long. Such a workpiece is supported by its ends between centers or chucks but, because of its size, it requires intermediate supports, steady rests, as it is being rotated. Generally, both the crankshaft journals and the crank pin journals (pins) must be ground. New grinding technology has the crankshaft rotated about its longitudinal axis so that the crank pin orbits around the crankshaft axis of rotation. A grinding wheel then moves in to grind the orbiting crank pin. Such an application places substantial loads on the steady rests in which the direction of the resulting force vectors on the steady rest are continually changing. In some cases, the force is so substantial as to cause the clamping members to separate.
The broad purpose of the present invention is to provide a self-centering clamping device that may be used for supporting either a cylindrical workpiece that is being ground or machined as it is being rotated, or in other applications such as for cutting tubing and the like, where the center line of the workpiece must be accurately maintained.
The preferred embodiment of the invention comprises a channel-shaped housing having a pair of spaced, parallel side plates, on a slide base. Two face-to-face plate-like clamping bars are slidably mounted on the slide base between the side plates. One clamping bar is longer than the other and supports a shoe beyond the center of rotation of the workpiece. The shorter clamping bar supports another shoe on the opposite side of the workpiece. The two clamping bars are cammed in opposite directions so that as the shorter (front) clamping bar is pushed toward the workpiece, the shoe on the longer (rear) clamping bar is pulled toward the workpiece. Both clamping bars slide on the base along a linear path of motion.
Each clamping bar has a cam slot disposed at an angle to the sliding motion of the bar. A power cylinder has an actuator plunger moveable along a path perpendicular to the sliding path of the clamping bars. The plunger is connected to camming rollers disposed in both of the slots in such a manner that as the plunger is moved in one direction, the clamping bars slide to close the distance between the clamping shoes. When the plunger is moved in the opposite direction, the two clamping bars are cammed in a release direction to open the clamping shoes.
A roller is carried between the side plates and engaged with the top edges of the two bars to constrain them against vertical relative motion when a substantial vertical grinding load is applied on the clamping shoes.
The preferred steady rest can be employed in various forms. For example, in one form a single hydraulic actuator moves the two clamping bars. An electrical motor or even a hand crank can be employed for camming the two clamping bars toward and away from their clamping positions.
In another embodiment, two hydraulic actuators are employed, one for each clamping bar. This version may be used for grinding bearing journals. In still another embodiment, three actuators are employed; one for each clamping bar, and a third for a pivotal arm that swings a third clamping shoe toward the work piece.
Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.